1. Field of the Invention
The present invention relates generally to a metal drawing process and, more particularly, to an improved lubrication system which is particularly well-adapted for one step deep drawing of metal articles such as steel sinks, tubs, automobile fenders and the like.
2. Prior Art
A drawing process is one wherein a relatively flat metal piece is deformed by compression between a pair of interfitting drawing tools, namely a punch and a die. The drawing process is performed on a press which positions the interfitting drawing tools at opposite ends of a path of travel, which moves the tools relative toward each other along the travel path to effect drawing of a flat blank placed along the travel path, and which moves the tools relatively apart to permit removal of the drawn part. As the tools close against the blank during drawing, the blank is deformed to a desired shape as complex stresses are imparted in the blank.
A problem of current times is that good drawing quality enameling steel is not readily available. In previous years, this product was made far more widely than it is now. Moreover, in previous years, competition tended to produce drawing quality enameling steel of greater uniformity and of better quality than is now available. As a result of these current day changes, the problem of providing effective lubrication systems for use in deep drawing operations is rendered far more difficult than it was only a few years ago.
In the manufacture of such deep drawn structures as deep bowl kitchen sinks, few manufacturers are able to draw a deep sink bowl from a single piece of steel because the required extensive deformation induces large, complex stresses which are not easily controlled or minimized. Stress reduction in such an operation has previously been attempted by the use of lubricants known as drawing compounds.
It is known to apply lubricants to the faces of the drawing tools to enable the metal blank to "flow" more readily during the drawing process, thereby reducing the stresses imparted in the blank. The lubricants used for such purposes are known as drawing compounds. These compounds must adhere to both the metal blank and to the drawing tools so that the compounds will continuously provide an uninterrupted lubricating film as the drawing process proceeds. Moreover, the compounds need to be washable so they can be easily but thoroughly removed from the surfaces of the newly formed sink or other deeply drawn part to enable the part to be properly enameled or otherwise finished.
Many conventional lubricants have been developed which are based on oils, greases, fats, soaps, and related products. Specially modified formulations are utilized in attempts to satisfy the requirements of a particular type of deep drawing operation. A drawing compound found to be reasonably suitable for a particular drawing operation is often found to be entirely unsuitable for use in a very similar type of drawing operation. Consequently, locating, testing and deciding upon the type of drawing compound to be used with a particular drawing operation can amount to a difficult and expensive task.
Very few of the commercially available drawing compound products have met the needs of deep sink bowl manufacturers. The products that have been found to be of reasonable utility are very expensive and they are not widely available. In at least one case the most effective product was proprietary in nature, protected by trade secret. When the manufacturer stopped its manufacture, the product was no longer available at any price.
The few conventional lubricants which have been found to be reasonably effective for use in the deep drawing of steel sinks have had other drawbacks. The operation of applying these compounds to blanks about to be drawn is time consuming, messy and wasteful. Moreover, the lubricants are not thoroughly removable from newly formed sinks by commerical washing techniques. Consequently, the lubricants tend to remain in the pores of the metal sink and to make satisfactory finishing such as enameling of the sinks difficult if not impossible. Still further, even with relatively effective conventional lubricants, sink manufacturers have experienced unacceptably high rates of rejection due to insufficient lubricating characteristics of the lubricant during drawing.
Recent proposals to overcome some of the foregoing drawbacks have suggested the use of dry plastic polymer films adhered to one or both sides of a metal blank which is to be drawn. Such proposals are inherently expensive, require special equipment to apply the dry film-forming resins, consume large amounts of space to carry out, and require unduly long handling times during drying of the applied resins. Moreover, special procedures must be instituted to effect removal of the resins following drawing operations and prior to subsequent surface treatment. Here again, extra equipment and handling are required.
Still another proposal has been to employ a single discrete sheet of commercially available polymer film placed against either side of a blank to be drawn. The use of non-adhered polymeric films is acknowledged to provide a lubricating function in drawing operations.
In spite of the above-described advances, there remains a need for an improved lubrication system for use in the drawing of sheet metal products. There is a need for a lubrication system which can be used uniformly with a wide variety of drawing situations, i.e., which does not require the selection or development of special formulations for each particular job. There is a need for a simple lubrication system which does not rely on proprietary, generally unavailable compositions; which is cost effective; which eliminates coating and removal steps and their attendant labor, equipment, and time expenditures; which eliminates waste and which provides the lowest possible rate of product rejections.